Apparatus for aligning a wafer

ABSTRACT

A method for aligning a wafer on a support member within a vacuum chamber includes increasing the pressure within the vacuum chamber to at least about 1 Torr before aligning the wafer. The wafer is introduced into the vacuum chamber on the support member, the pressure is increased to at least about one Torr, and the support member is lifted into a shadow ring that has a frustoconical inner cavity constructed to funnel the wafer to a centered, aligned position.

This is a divisional of application Ser. No. 08/893,461 filed on Jul.11, 1997. Now U.S. Pat. No. 6,063,440 issued May 16, 2000.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of semiconductor waferprocessing equipment. More particularly, the present invention relatesto a method and apparatus for aligning a wafer on a wafer supportmember.

2. Background of the Related Art

In the fabrication of integrated circuits, the various processes, suchas physical vapor deposition (PVD), chemical vapor deposition (CVD), andetch processes, are often carried out in a vacuum environment to, amongother things, reduce the particulate level to which the wafers areexposed. Wafers are introduced into a vacuum processing system through aloadlock where robots within the vacuum processing system move thewafers from the loadlock into a transfer chamber and then sequentiallythrough the system positioning the wafers in a series of processingchambers.

The processing steps carried out within the vacuum chambers typicallyrequire the deposition, or etching of multiple metal, dielectric andsemiconductor film layers on the surface of a wafer. During theseprocessing steps, one must properly align and secure the wafer in theprocessing chamber in which the desired deposition or etch process isperformed.

Typically, the wafer is supported in the chamber on a support member,commonly called a susceptor or pedestal. The wafer is placed on orsecured to, the upper surface of the support member prior to thedeposition or etch process. To ensure proper processing of the wafer,the wafer must be properly aligned relative to the support member. Theposition of the support member in the chamber is selected to provide adesired spacing and relative geometry between the generally planarsurface of the wafer and other portions of the process chamber such as agas plate in a CVD process or a target in a PVD process.

Generally, a shadow or clamp ring is used to shield the edge of a waferand/or, in the case of a clamp ring, secure the wafer to the supportmember. Although the present invention is equally applicable to bothshadow rings and clamp rings, the following description will referprimarily to shadow rings such as those typically used in CVD processes.In addition to acting as a shield, shadow rings also function in wafercapturing or alignment on the support member. Wing members extenddownwardly and outwardly from the shadow ring to form a funnel. As thesupport member moves the wafer upward into the processing position, thesupport member moves the wafer into the funnel which directs the waferinto alignment with the shadow ring and the support member.Consequently, the funnel applies vertical and lateral forces to thewafer when the slanted wing members achieve lateral alignment of amisaligned wafer with the shadow ring and support member as the supportmember moves the wafer to the top end of the funnel and the shadow ringsettles on the support member.

A primary goal of wafer processing is to obtain as many useful die aspossible from each wafer. Many factors influence the processing ofwafers in the chamber and effect the ultimate yield of die from eachwafer processed therein including the existence of contaminants withinthe chamber that can attach to the wafer and contaminate one or more dietherein. The processing chambers have many sources of particlecontaminants which, if received on the wafer, reduce the die yield. Onesource of particulate contamination occurs when a misaligned wafer isintroduced into the chamber. As the wing members of the shadow ringalign with the wafer, the wafer slides on the flat surface of thesupport member and, due to the frictional forces between the wafer andthe support member, may create particulate contaminants. In some cases,the frictional forces between the wafer and the support member cause themisaligned wafer to actually move the shadow ring, thereby preventingproper alignment of the wafer and reducing repeatability of the zone ofexclusion shielded by the shadow ring and the process.

Prior efforts aimed at reducing the creation of particles have reducedthe alignment movement of the wafer on the support member and simplyincreased the amount of overhang by the shadow ring. In this way, theshadow ring is able to cover the wafer without substantial movement ofthe wafer. One way that this is accomplished is by increasing thediameter of the shadow ring funnel upper end so that this diameter islarger relative to the diameter of the wafer and the support member.Thus, rather than substantially moving the wafers to align them, thesesystems simply accept a greater misalignment and accept greater coverageof the wafer upper surface area.

However, a second factor influencing the processing of wafers in thechamber and affecting the ultimate yield of die from each waferprocessed therein is the repeatability of the positioning of the waferand the area covered by the shadow ring. The wafer must be properlyaligned relative to the support member and the shadow ring to ensurethat the film is properly deposited on the wafer. Therefore, these priorefforts that avoid alignment of the wafer and cover more surface areaare not acceptable.

It would, therefore, be desirable to provide a relatively simple systemand method for reducing the coefficient of friction between the supportmember and the wafer that would allow alignment of the wafer withoutsubstantial particle generation.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide arelatively simple apparatus and method for reducing the frictionalforces between the support member and the wafer. It is another object ofthe invention to enhance repeatability and to provide a shadow ring thatcovers a minimal area of the upper surface of the wafer. Yet anotherobject of the invention is to provide a system and method for aligning awafer that is relatively inexpensive, efficient, simple to implement,and reliable. Other objects of the invention will become apparent fromtime to time throughout the specification and claims as hereinafterrelated.

The present invention provides methods and apparatuses for aligning awafer on a support member in a vacuum chamber. In one aspect of theinvention, the method comprises the steps of introducing the wafer intothe vacuum chamber, increasing the pressure within the vacuum chamberand moving the wafer into alignment with a support member and/or shadowring.

In another aspect, the method comprises providing a shadow ring having alower portion that is outwardly tapered for receipt of a wafer and anupper aperture having a diameter that is slightly less than the outerdiameter of the wafer, introducing the wafer into the vacuum chamber andonto the support member, increasing the pressure within the chamber, andsubsequently moving the support member towards the shadow ring so thatthe shadow ring aligns the wafer on the support member.

In accordance with the methods, the apparatus for aligning a wafer on asupport member in a vacuum chamber is an apparatus comprising a supportmember positioned within the vacuum enclosure and having a waferreceiving surface thereon, a shadow ring located within the vacuumchamber, a gas supply in fluid communication with the vacuum chamber,and a gas flow controller that controls the flow of gas to the vacuumchamber and, thereby, regulates the pressure within the vacuum chambersuch that, after the wafer is positioned on the support member andbefore the wafer is raised into the shadow ring, the gas flow controllerraises the pressure within the chamber to about 1 Torr. The shadow ringused in this apparatus comprises an upper shield portion defining acircular aperture therethrough, the circular aperture having a diameterthat is slightly less than the outer diameter of the wafer, a lowerportion extending from the upper shield portion having an annular crosssection defining a frustoconical inner cavity, the diameter of the innercavity decreases from a lower mouth aperture to an upper end, and thediameter of the upper end of the inner cavity is slightly greater thanthe outer diameter of the wafer.

In each of these methods and apparatuses, the pressure is preferablyraised to a pressure greater than about 1 Torr and more preferably to apressure between about 1 Torr and 100 Torr and most preferably betweenabout 1 Torr and 10 Torr. Further, the pressure is raised is toapproximately equal to or less than the process pressure. Also, thepressure between the wafer and the support member is preferably equal toor greater than the pressure in the chamber before the wafer is aligned.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features, advantages andobjects of the present invention are attained and can be understood indetail, a more particular description of the invention, brieflysummarized above, may be had by reference to the embodiments thereofwhich are illustrated in the appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 is a partial cross sectional view of the vacuum chamber.

FIG. 2 is a schematic drawing of the vacuum chamber and the pressurecontrol system.

FIG. 3 is a cross sectional view of a typical support member having awafer thereon that is partially covered by a shadow ring.

FIG. 4 is a partial, cross sectional view of a shadow ring, a wafer, anda support member showing the wafer misaligned on the support member asthey enter the inner cavity of the shadow ring.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIG. 1, the present invention relates to a method andapparatus for aligning a wafer 20 on a support member 60 in a vacuumchamber 30. The alignment apparatus is depicted generally as 10.

The preferred embodiment described below refers to an alignmentapparatus 10 that uses a shadow ring 40 to align the wafer 20 on thesupport member 60. However, the invention is not limited to this preciseform of apparatus for it may apply to any number of alignmentmechanisms. As previously mentioned, the term “shadow ring,” as usedherein, refers generally to both shadow rings and clamp rings.

FIG. 1 shows a typical vacuum chamber 30 defined by an outer body 34.The vacuum chamber 30 houses a support member 60 that may take the formof a pedestal or susceptor mounted on a generally vertically orientedshaft 62. The support member 60 serves to support a wafer 20 on its flatupper supporting surface 69. The support member 60 also includes a stepformation 68 formed on its outer perimeter to receive and support ashadow ring 40 and includes four finger apertures 66.

In a typical vacuum chamber 30, the pressure within the vacuum chamber30 is controlled by a pressure control system such as the one shownschematically in FIG. 2. In this system, a gas supply 170 is provided influid communication with the vacuum chamber 30. A gas flow controller180 positioned intermediate the gas supply 170 and the vacuum chamber 30controls the flow from the gas supply 170 to the vacuum chamber 30.Using a predetermined set of instructions, the gas flow controller 180selectively provides a flow of gas to the vacuum chamber 30. As the gasflows into the vacuum chamber 30, the pressure within the vacuum chamber30 increases. In this way, the gas flow controller 180 controls thepressure within the vacuum chamber 30. It is possible to provide the gasto the chamber 30 through the support member 60 to the back side of thewafer 20. When provided to the back side of the wafer 20, the gascreates a pressure between the wafer 20 and the support member 60 thatis initially greater than the pressure in the chamber 30. This back sidegas may be provided, for example, by a bypass line 200 that providescommunication from the gas flow controller 180 to the upper surface 64of the support member 60 between the support member 60 and the wafer 20.

FIG. 1 also illustrates a wafer lifting finger 90 received in a fingeraperture 66 passing through the body of the support member 60.Typically, the processing chamber would include four such liftingfingers 90. These lifting fingers 90 operate to lift the wafer 20 clearof the upper supporting surface 69 of the support member 60 afterprocessing. This removal of the wafer 20 is achieved by means of aconventional processing apparatus robot arm (not shown) which enters thevacuum chamber 30 through the slit valve opening 36. The same robot armis also used to insert the wafers 20 into the vacuum chamber 30. Thelifting fingers 90 are movable vertically under action of a liftingmechanism 92 of which only the upper portion is shown.

A shadow ring 40 housed within the vacuum chamber 30 operates to providean exclusionary zone where no deposition occurs at the edge of the wafer20. The shadow ring 40 also operates to force a misaligned wafer 20 intoalignment as the support member 30 moves from a lowered, or idle,position to a raised, or processing, position. When the support member30 is in the lowered position, the shadow ring 40 is supported aroundits perimeter by an outer support ring 38 that is, in turn, supported bya conventional pumping plate 39 attached to the vacuum chamber 30.Together, the two rings, 40 and 38, divide the vacuum chamber 30 intoupper and lower sections, 30 a and 30 b respectively.

During processing, the support member 60 moves upward into a raisedposition lifting the shadow ring 40. The shadow ring 40 has a lowerportion 42 that rests on the upper surface 64 of the support member 60and supports the upper shield portion 50 of the shadow ring 40 above theupper surface of the wafer 20. Preferably, the shield portion 50 is heldabout 5 to 10 mils above the wafer 20. The upper shield portion 50 ofthe shadow ring 40 defines a circular upper aperture 46 therethrough.The diameter of the upper aperture 46 may be slightly less than theouter diameter of the wafer 20 to form the exclusionary zone on thewafer 20. However, new processes may require no overhang of the shadowring 40 over the wafer 20. In one typical processing operation, the stepformation 68, shown in FIG. 1, is in the range of 3.8 to 3.9 mm high,the shadow ring 40 is in the range of 5 to 5.1 mm thick, and theoverhanging portion is in the range of 0.8 to 0.9 mm thick. Theoverhanging portion defines an exclusionary zone of about 3 to 5 mmabout the edge of the wafer 20. However, in the preferred embodiment,this exclusionary zone is no greater than 1.5 mm from the edge of thewafer 20. To accommodate the current industry standards, theexclusionary zone at any one edge is preferably about 1.5 mm or less.This relatively small exclusionary zone is necessary to allow depositionon the wafer 20 at a position 1.5 mm from the wafer edge. Industrystandards demand a film thickness at 1.5 mm from the wafer edge that isat least 90 percent of the film thickness at the wafer center. Nodeposition is allowed on the beveled edge of the wafer 20. Therefore,for a typical wafer 20 having a 0.5 mm chamfer about its edge, thisallows a deviation of only about 1 mm from center. As used herein, alldimensions account for thermal expansion and are representative ofmeasurements at process temperatures.

Preferably, a purge gas is directed through the support member 60 aboutthe periphery of the wafer 20. The purge gas flows between the shadowring 40 and the wafer 20 to help shield the exclusionary zone of thewafer 20.

A lower portion 42 of the shadow ring 40, as shown in FIG. 4, extendsdownwardly from the upper shield portion 50. The lower portion 42 has anannular cross section throughout its length and defines a frustoconicalinner cavity 44 therein that is concentric with the upper aperture 52.Because wafers 20 are circular in shape, the support member 60 iscircular as is the inner cavity cross section. The diameter of the innercavity 44 decreases from the lower mouth portion 46 to the upper end 48of the inner cavity 44 to form a funnel-like structure for aligning thewafer 20 on the support member 60. Accordingly, the surface of the innercavity 44 is relatively smooth to facilitate the sliding receipt andabutment of the wafer 20 in the inner cavity 44. To allow receipt of thewafer within inner cavity 44 and to properly align the wafer 20 with theshadow ring 40, the diameter of the upper end 46 of the inner cavity 44is slightly greater than and, preferably, approximately equal to theouter diameter of the wafer 20. As previously mentioned, currentindustry practice demands that the thickness of the deposited film at aposition 1.5 mm from the edge of the wafer 20 be 90 percent of thethickness at the center of the wafer 20. Accordingly, the wafer 20 mustbe aligned so that the shadow ring overhangs the wafer 20 by no morethan 1.5 mm about its full periphery so that the film will be allowed todeposit on the wafer 20 at 1.5 mm from the edge of the wafer 20.Therefore, the diameter of the upper end 46 of the inner cavity 44 ispreferably at most only slightly more than 3 mm greater than the upperaperture 52 and only slightly greater than the outer diameter of thewafer 20 to ensure that the edge of the wafer 20 is within 1.5 mm of theperiphery of the upper aperture 52. In this way, the shadow ring 40 onlyoverhangs the wafer 20 at most by about 1.5 mm about the full peripheryof the wafer 20. Because the wafer 20 rests on the upper surface 64 ofthe support member 60 and the wafer 20 is relatively thin, the outerdiameter of the support member 60 must be sufficiently small that it canalso be positioned proximal the upper end 52 of the inner cavity 44.However, to provide proper support for the wafer 20, the support member60 must cover substantially the full area of the wafer 20. Therefore,the wafer must occupy most of the upper surface area of the supportmember 60.

As shown in FIG. 1, once positioned in the vacuum chamber 30, a wafer 20rests on the upper supporting surface 69 of the support member 30. Thisplacement is made with the support member 60 in its lowered position.Before processing may begin, the wafer 20 must first be raised by thesupport member 60 to the raised position. It is during the movement fromthe lowered position to the raised position that any misalignment of thewafer 20 is corrected and the wafer 20 is aligned. As the support member60 moves upward from the lowered position, a misaligned wafer 20contacts the inner cavity 44 of the shadow ring 40 at a positionintermediate the upper end 48 and the lower mouth portion 46. FIG. 4illustrates a misaligned wafer 20 on the support member 60. The point ofcontact is dependent upon the magnitude of the misalignment. Preferably,there is no misalignment. As the support member 60 continues to moveupward, the angled side of the frustoconically-shaped inner cavity 44exerts a lateral force on the edge of the wafer 20 forcing the wafer 20into alignment. Consequently, when the support member 60 reaches itsraised position so that the wafer 20 is at the upper end 48 of the innercavity 44 of the shadow ring 40, the wafer 20 is aligned due to therelative diameters of the wafer 20 and the shadow ring components. Whenin this raised position, depending upon the type of process involved,the outer portion of the wafer 20 may either bear against the shadowring 40 and slightly lift the shadow ring 40 under action of the supportmember 60 or may rest on the shoulder 68 of the support member 60 and,thereby, leave a small gap between the shadow ring 40 and the wafer 20.For convenience, the application refers primarily to those processeswherein the wafer 20 does not contact the shadow ring 40 although thepresent invention is applicable to all processes. With the supportmember 60 in the raised position, the outer portion of the wafer 20 iscovered by the upper shield portion 50 of the shadow ring 40.

However, as mentioned previously, the sliding movement of the wafer 20on the support member 60 during alignment creates particles within thevacuum chamber 30. These particles are generated as a result of thefriction between the wafer 20 and the support member 60 which isgenerally characterized by the coefficient of friction of the interfacemultiplied by the weight of the wafer 20. Other forces acting upon thewafer 20 also affect the magnitude of the frictional forces. Forexample, vacuum chucking may affect the friction between the wafer 20and the support member 60. Likewise, the downward component of the forceexerted by the frustoconical inner cavity 44 increases the frictionalforces between the abutting surfaces. Nevertheless, the friction forcebetween the surfaces equals the coefficient of friction between thesurfaces multiplied by the downward force exerted on the wafer 20whatever their source. Generally, the weights of the wafers 20 arerelatively constant. Greater frictional forces on the wafer 20 and thesupport surface 60 cause greater particle generation and decrease theenergy efficiency of the system. In addition, high frictional forces maycause misalignment and may cause the wafer 20 to move the shadow ring 40out of alignment, rather than the shadow ring 40 moving the wafer intoalignment, if the lateral force applied to the wafer 20 by the shadowring is insufficient to overcome the frictional forces. For the purposesof the present application, the relevant normal and frictional forcesare generally characterized by the following formulas respectivelywherein N represents the normal force applied to the wafer 20, F is thefrictional force applied to the wafer 20, G is the weight of the wafer20, A is the surface area of the wafer 20, P₀ is the pressure in thechamber 30, P₁ is the pressure between the wafer 20 and the supportmember 60, and μ is the coefficient of friction.

N=G−(P₁−P₀)A

F=μN=μ(G−(P₁-P₀)A)

Thus, the normal force is equal to the weight of the wafer 20 less theforce created by the pressure differential on the top and bottomsurfaces of the wafer 20. The force created by this pressuredifferential equals the difference between the pressure between thewafer 20 and the support member 60 and the pressure in the chamber 30multiplied by the surface area of the wafer 20. The frictional forcesequal the normal forces multiplied by the coefficient of friction.

Reducing the frictional forces between the wafer 20 and the supportmember 60 reduces the number of particles generated when the wafer 20 ismoved on the support member 60. Accordingly, in order to reduce thenumber of particles generated, the coefficient of friction or the normalforce between the wafer 20 and the support member 60 must be reduced.The present invention accomplishes this by increasing the pressurewithin the vacuum chamber 30 to at least about one Torr. Empiricalstudies, which are more fully discussed below, have shown thatincreasing the pressure within the vacuum chamber 30, so that thepressure between the wafer 20 and the support member 60 is equal to orgreater than the pressure in the vacuum chamber 30, reduces thefrictional forces between the wafer 20 and the support member 60. Inorder for this decrease in frictional force to occur, one of two thingsmust happen. One possibility is that the increased pressure somehowlowers the coefficient of friction (e.g., by possibly creating a cushionof gas between the wafer 20 and the support member 60). Anotherpossibility is that the increased pressure somehow lowers the normalforce on the wafer 20. Regardless of the manner in which increasing thepressure affects the frictional forces, the result is that thefrictional forces are reduced and, thus, the wafer 20 may be moved onthe support member 60 with less resistance and less particle generation.The resulting decrease in frictional force allows freer movement of thewafer 20 on the support member 60 and, thereby, reduces the resultingscratches and generated particles. Gas from the gas supply 170 isintroduced into the vacuum chamber 30 to increase the pressure therein.The gas may be introduced generally into the chamber 30 or through gasinlets positioned in the upper surface 64 of the support member 60. Itis in this latter case that the pressure below the wafer 20 is greaterthan the pressure above the wafer 20.

Therefore, the method of the present invention involves increasing thepressure within the vacuum chamber 30 to at least about one Torr beforemoving the wafer 20 on the support member 60 for alignment. Typically,the pressure within the vacuum chamber 30 when the wafer 20 isintroduced therein is about one milliTorr or less. The wafer is, thus,introduced into the vacuum chamber 30 onto the support member 60 whichis in a lowered position. The support member 60 is then raised to thelower mouth aperture 46 of the shadow ring 40. However, before raisingthe support member 60 to the processing position the pressure within thevacuum chamber 30 is increased to at least about one Torr. Of course,this step of increasing the pressure may take place at any time beforethe support member 60 is raised into the inner cavity 44 of the shadowring 40. Preferably, the pressure is raised to between about 1 Torr and100 Torr or, more preferably, between about 1 Torr and 10 Torr andapproximately equal to or less than the operating pressure of theprocess. The operating pressure of the process is the pressure at whichthe process, such as a chemical vapor deposition process, is carried outin the vacuum chamber 30. Also, before raising the support member 60 tothe raised position, the pressure between the wafer 20 and the supportmember 60 is provided so that the pressure between the wafer 20 and thesupport member 60 is approximately equal to or greater than the pressurein the vacuum chamber 30. Once the pressure in the vacuum chamber 30 issufficiently raised and the pressure beneath the wafer 20 is equalized,the support member 60 is raised to the raised, or processing, position.As previously discussed, when the support member 60 moves into theshadow ring 40, any misaligned wafer 20 will contact the angled sides ofthe inner cavity 44 which will force the wafer 20 into alignment. Afterthe support member 60 is in the raised position and the wafer 20 isaligned, the pressure within the vacuum chamber 30 may be altered asneeded.

As previously described, the pressure within the vacuum chamber 30 ismanipulated by a gas supply 170 and a gas flow controller 180. Inoperation, the gas flow controller 180 uses predetermined set ofinstructions to adjust the pressure within the vacuum chamber 30 asneeded. A vacuum pump 190, or series of vacuum pumps 190, are used toevacuate the vacuum chamber 30.

EXAMPLE

This system has been tested to determine its effectiveness as follows. Amisaligned wafer 20 was positioned upon a support member 60 in a vacuumchamber 30 and was raised from a lowered position to a raised position.The test was conducted under vacuum conditions (i.e., moving the wafer20 without first increasing the pressure in the chamber) and underpressurized conditions (i.e., moving the wafer 20 only after increasingthe pressure in the chamber). When tested under pressurized conditions,the tests were conducted with both the pressure beneath the wafer 20equal to and greater than the pressure in the chamber 30. In both ofthese pressurized condition tests, the results were essentially thesame. The wafers 20 were then inspected using a SURISCAN 6200manufactured by Tencor Instruments to determine the number of particlesgenerated as a result of the wafer 20 moving on the support member 60.The results revealed that, without first increasing the pressure in thechamber, alignment of the wafer generated approximately 50 to 200particles when the wafer 20 contacted the shadow ring and approximately5000 backside particles. In addition, without first increasing thepressure in the chamber, the shadow ring 40 often moved with the wafer20 as the support member 60 lifted the shadow ring 40 due to thefrictional forces holding the wafer 20 to the support member 60. Thisresulted in a misaligned wafer 20 and reduced repeatability of theprocess. However, using the present invention, wherein the pressure israised to at least about one Torr before moving the wafer 20, themovement of the wafer 20 on the support member 60 generated onlyapproximately Twenty (20) particles when the wafer 20 contacted theshadow ring 40 and less than 2000 backside particles. Further, themisaligned wafer 20 moved on the support member 60 more readily and was,therefore, properly centered which increased repeatability of the edgeexclusion and the process.

While the foregoing is directed to the preferred embodiment of thepresent invention, other and further embodiments of the invention may bedevised without departing from the basic scope thereof, and the scopethereof is determined by the claims which follow.

What is claimed is:
 1. An apparatus for aligning a wafer in a processing chamber, comprising: a support member positioned within the processing chamber and having a wafer receiving surface thereon; a shadow ring located within the processing chamber, the shadow ring comprising: an upper shield portion defining a circular upper aperture therethrough, the upper aperture having an inner diameter and a wafer shielding surface disposed outwardly from the inner diameter of the upper shield portion; a lower portion extending from the upper shield portion and having an annular cross section defining a frustoconical inner cavity, wherein the diameter of the inner cavity decreases from a lower aperture to an upper end, and the diameter of the upper end of the inner cavity is greater than the inner diameter of the shield portion; a gas supply in fluid communication with the processing chamber; and a gas flow controller having a predetermined set of instructions to regulate pressure within the processing chamber such that, after a wafer is positioned on the support member and before the wafer is raised into the shadow ring, the predetermined set of instructions direct the gas flow controller to increase the pressure within the processing chamber and to provide a pressure between the wafer and support member to a pressure greater than or equal to the pressure within the processing chamber to align the wafer with the shadow ring and support member.
 2. The apparatus of claim 1, wherein the gas flow controller increases the pressure within the processing chamber to about 1 Torr.
 3. The apparatus of claim 1, wherein the gas flow controller increases the pressure within the processing chamber to a pressure between about 1 Torr and about 100 Torr.
 4. The apparatus of claim 1, wherein the gas flow controller increases the pressure within the processing chamber to a pressure between about 1 Torr and about 10 Torr.
 5. The apparatus of claim 1, wherein the gas flow controller increases the pressure within the processing chamber to a pressure that is at least about 1 Torr and below an operating pressure.
 6. The apparatus of claim 1, wherein the difference between the inner diameter of the upper aperture in the upper shield portion and the diameter of the upper end of the inner cavity is no greater than about 5 millimeters.
 7. The apparatus of claim 1, wherein the difference between the inner diameter of the upper aperture in the upper shield portion and the diameter of the upper end of the inner cavity is no greater than about 3 millimeters.
 8. The apparatus of claim 1, wherein the diameter of the upper end of the inner cavity is substantially equal to the diameter of the upper end of the inner cavity.
 9. An apparatus for aligning a wafer in a processing chamber, comprising: a support member positioned within the processing chamber having a wafer receiving surface thereon; a shadow ring located within the processing chamber, the shadow ring adapted to align a wafer; a gas supply in fluid communication with the processing chamber; and a gas flow controller having a predetermined set of instructions to regulate pressure within the processing chamber such that, after a wafer is positioned on the support member and before the wafer is raised into the shadow ring, the predetermined set of instructions direct the gas flow controller to increase the pressure within the processing chamber and to provide a pressure between the wafer and support member to a pressure greater than or equal to the pressure within the processing chamber to align the wafer with the shadow ring and support member.
 10. The apparatus of claim 9, wherein the shadow ring comprises: an upper shield portion defining a circular upper aperture therethrough, the upper aperture having an inner diameter and a wafer shielding surface disposed outwardly from the inner diameter of the upper shield portion; and a lower portion extending from the upper shield portion and having an annular cross section defining a frustoconical inner cavity, wherein the diameter of the inner cavity decreases from a lower aperture to an upper end, and the diameter of the upper end of the inner cavity is greater than the inner diameter of the shield portion.
 11. The apparatus of claim 10, wherein the diameter of the upper end of the inner cavity is substantially equal to the diameter of the upper end of the inner cavity.
 12. The apparatus of claims 10, wherein the difference between the diameter of the upper aperture in the upper shield portion and the diameter of the upper end of the inner cavity is no greater than about 3 millimeters.
 13. The apparatus of claim 10, wherein the difference between the diameter of the upper aperture in the upper shield portion and the diameter of the upper end of the inner cavity is no greater than about 5 millimeters.
 14. The apparatus of claim 9, wherein the gas flow controller increases the pressure within the processing chamber to about 1 Torr.
 15. The apparatus of claim 9, wherein the gas flow controller increases the pressure within the processing chamber to a pressure between about 1 Torr and about 100 Torr.
 16. The apparatus of claim 9, wherein the gas flow controller increases the pressure within the processing chamber to a pressure between about 1 Torr and about 10 Torr.
 17. An apparatus for aligning a wafer in a processing chamber, comprising: a support member positioned within the processing chamber and having a wafer receiving surface thereon; a shadow ring located within the processing chamber, the shadow ring comprising: an upper shield portion defining a circular upper aperture therethrough, the upper aperture having an inner diameter and a wafer shielding surface disposed outwardly from the inner diameter of the upper shield portion; a lower portion extending from the upper shield portion and having an annular cross section defining a frustoconical inner cavity, wherein the diameter of the inner cavity decreases from a lower aperture to an upper end, and the diameter of the upper end of the inner cavity is greater than the inner diameter of the shield portion; a gas supply in fluid communication with the processing chamber; and a gas flow controller having a predetermined set of instructions to regulate pressure within the processing chamber such that, after a wafer is positioned on the support member and before the wafer is raised into the shadow ring, the predetermined set of instructions direct the gas flow controller to increase the pressure within the processing chamber that is at least about 1 Torr and below an operating pressure and to provide a pressure between the wafer and support member to a pressure greater than or equal to at least about 1 Torr to align the wafer with the shadow ring and support member.
 18. The apparatus of claim 17, wherein the diameter of the upper end of the inner cavity is substantially equal to the diameter of the upper end of the inner cavity.
 19. The apparatus of claim 17, wherein the difference between the diameter of the upper aperture in the upper shield portion and the diameter of the upper end of the inner cavity is no greater than about 3 millimeters.
 20. The apparatus of claim 17, wherein the difference between the diameter of the upper aperture in the upper shield portion and the diameter of the upper end of the inner cavity is no greater than about 5 millimeters. 